Process for the Extraction of Metal Pollutants from Treated Cellulosic Biomass

ABSTRACT

The present invention relates to a process for extracting oxidised metal pollutants from treated cellulosic or lignocellulosic biomass to recover the metal. The treatment also generates a cellulosic or lignocellulosic biomass which can to be used as a feedstock for biofuel, for making cellulose containing materials, and provides a source of other renewable chemicals.

The present invention relates to a process for extracting oxidised metalpollutants from treated cellulosic or lignocellulosic biomass to recoverthe metal. The treatment also generates a cellulosic or lignocellulosicbiomass which can to be used as a feedstock for biofuel, for makingcellulose containing materials, and provides a source of other renewablechemicals.

A significant portion of wood used in the construction industry istreated with metal based preservatives. This is done to protect the woodfrom attack by microbes and insects during service. The preservativescontain copper (II) and sometimes also chromium (VI) (as chromate) andarsenic (V) (as arsenic pentoxide). Other metal pollutants are alsofound in wood such as zinc (II), iron (II/III) and lead (II). The mainapplications for preservative treated wood are decks, fences, landscapearchitecture, playground equipment, docks, marinas, utility poles,bridges, highway sound barriers, roller coasters, wood foundations andmine shafts. These preservative formulations are toxic: copper (II) istoxic to aquatic life and arsenic (V) and chromium (VI) are known to bevery toxic to any multicellular life including humans. Leaching fromin-service-material is limited, although public health concerns havebeen raised. Apart from this, the non-degradability of the wood andtoxicity of the preservatives pose a definitive problem when the wood istaken out of service.

Common preservative formulations used are alkaline copper quaternary(ACQ), copper azole (CA, Tanalith E) and micronized copper quaternary(MCQ), which all contain substantial amounts of copper (up to 3700 ppm).Chromated copper arsenate (CCA, Tanalith C), a mixture of CuO, CrO₃ andAs₂O₅ has been used extensively between the 1930s until the early 2000s.Timber treated with CCA can contain over 5000 mg kg⁴ of arsenic (V) andchromium (VI). This is the most hazardous wood treatment, hence CCA usewas heavily curtailed in Europe and the US in 2003-2004. However, CCAtreated timber still in service will pose a substantial problem for thenext 20-40 years. Reportedly, up to 2.5×10⁶ m³ a⁻¹ of spent CCA-treatedwood will be removed from service in the next 20 years in Canada. It hasbeen estimated that 6-10×10⁶ m³ a⁻¹ of CCA-treated wood waste will beproduced in the USA by 2030.

The treated timber is classified as hazardous waste and cannot bedirectly used in biomass-to-heat conversion or recycled into panelboards or similar, thus incurring high costs for specialist disposal,such as landfilling. Copper (II) only treated timber may be incineratedin monitored specialist boilers and the waste reduced to metalcontaining ash. In contrast, incineration of arsenic (V) containing woodis problematic, as the arsenic (V) compounds generated during thermaltreatment are volatile and at least partially emitted into theatmosphere.

The following recovery methods of the metal additives from the treatedwood are in being used or currently explored:

-   -   (1) Controlled landfill        -   Landfills that are not in contact with the ground water            table are deemed suitable for disposal of treated wood            waste. However, landfill sites are becoming scarcer and            landfilling is becoming expensive.    -   (2) Thermal treatment and disposal of metal enriched ash        -   Boilers for thermal treatment of hazardous timber are not            operated in the UK due to high demand on furnace            specifications and monitoring (Regional Market Assessment            for Wood Waste for North East England, 2007). However,            thermal treatment may be feasible for wood treated with the            newer, copper only, preservatives. Copper compounds are            non-volatile and thus only a small percentage escapes as fly            ash into the atmosphere upon combustion of the contaminated            biomass (less than 7%). Processes deriving value from            combustion, gasification or pyrolysis do not currently            exist.    -   (3) Leaching and disposal of chemically precipitated metal ions        -   Leaching of the oxidised metals from the wood has been            proposed. Options discussed in the literature are            -   a. Leaching with dilute acid solution or aqueous                solutions containing chelating agents            -   b. Complete dissolution of waste wood in concentrated                sulfuric acid        -   The metal-containing effluents are treated as heavy metal            contaminated waste water (metal ions removed e.g. by            flocculation and precipitation). Recovered wood can be            incinerated as normal waste wood if the metal content is            sufficiently low. The recovered wood cannot be used as a            source of biofuel as the wood is decomposed during the            process and not suitable for subsequent use in the            saccharification process. Electrodeposition of Cu^(II) from            aqueous solution has been demonstrated recently. A recent            study presented insights obtained from operating a pilot            plant and the associated techno-economic model for dilute            acid-leaching. It was estimated that the operating cost            would be $250-289 t⁻¹ of treated wood. This shows that metal            extraction should be integrated with a value-adding            application.

The mentioned decontamination methods for metal containing timber arecostly, in the area of $180 t⁻¹ waste timber. On the other hand, cost ofvirgin wood feedstock for biofuel production is estimated to be $80 t⁻¹.Currently, there are a handful of commercial-scale cellulosic biofuelplants in operation, all using virgin biomass (mostly agriculturalresidues and energy grasses) and steam based pre-treatment technologies.

The use of contaminated waste wood as feedstock for a biorefinery wouldhence eliminate a waste management problem and increase the economicviability of lignocellulosic biomass for biofuel and biochemicalproduction. Electrochemical recovery of the metals in a useful elementalform would further add value.

Lignocellulosic biomass, such as wood, consists of 3 major componentsarranged in an intricate, yet physically and chemically stable material.Approximately 40% of wood is cellulose. Cellulose is long chains ofglucose arranged infibrils. They give wood its high strength andstiffness. Hemicellulose, 25 weight % of the material, acts as a fillermatrix that binds the cellulose fibrils together. Lignin, alsoapproximately 25% of the material, is a glue infused into the cellulosehemicellulose matrix, conferring elasticity and water-proofness.Cellulose and hemicellulose are long chains composed of sugars, whilelignin's repeat units contain aromatic rings. For cellulosic biofuelproduction, the lignocellulosic matrix is opened up duringpre-treatment/fractionation (at elevated temperature). A separatefraction of cellulose is obtained. The sugar molecules can be releasedfrom washed cellulose using an enzymatic hydrolysis step. The resultingsugar solution can be converted to biofuels or other biochemicals byfermentation. If a preservative treated lignocellulosic biomass sourcewas used, the presence of the metals e.g. copper from the preservativeswould kill the microbes used in the fermentation step. Therefore, onlyvirgin (untreated) biomass sources have been used to date. The ligninpresent in the lignocellulosic biomass can be used for energy recoveryand production of renewable materials such as resins, polyols, carbonfibres and chemicals, depending on the extraction conditions and purity.

The fractionation of cellulose and lignin from lignocellulosic biomassusing ionic liquids has been previously described in WO 2012/080702 andWO2014/140643.

The present invention describes a process of extracting metals fromtreated cellulosic or lignocellulosic biomass, such as wood, using anionic liquid (IL). The ionic liquids fractionate metal containingcellulosic or lignocellulosic biomass waste into a cellulose rich solidmaterial, and a liquid phase. The liquid phase comprises a hemicellulosefraction and a lignin fraction, and retains the metals in the ILsolution. The cellulose rich material can be used to produce biofuelsand plant derived chemicals. The metal, and optionally the lignin, canalso be recovered from the IL, and the IL can be recycled.

Thus in the first aspect the invention provides a process for theextraction of metal pollutants from treated cellulosic biomasscomprising contacting the treated cellulosic biomass with an ionicliquid, said ionic liquid comprising an anion and an organic cation. Asused herein an “organic” cation refers to a cation containing carbon andhydrogen and optionally one or more heteroatoms such as oxygen,nitrogen, phosphorous and sulfur.

“Extraction” as used herein refers to the removal of metal ions from thetreated cellulosic or lignocellulosic biomass. The metal ions dissolvein the ionic liquid. The extraction process removes sufficient metal sothat fermentation of the cellulose rich material produced is notinhibited by the presence of the metal pollutants. At least 50% of themetal present in the treated cellulosic or lignocellulosic biomass isremoved, more preferably at least 60%, 70%, 75%, 80%, 85%, 90%, 95% or99% of the metal present. Most preferably the process removes at least85% of the metal present.

As used herein the term “cellulosic” or “lignocellulosic biomass” refersto living or dead biological material that can be used in one or more ofthe disclosed processes. It can comprise any cellulosic orlignocellulosic material and includes materials comprising cellulose,and optionally further comprising hemicellulose, lignin, starch,oligosaccharides and/or monosaccharides, biopolymers, naturalderivatives of biopolymers, their mixtures, and breakdown products. Itcan also comprise additional components, such as protein and/or lipid.The biomass can be derived from a single source, or it can comprise amixture derived from more than one source. Some specific examples ofbiomass include, but are not limited to, bioenergy crops, agriculturalresidues, municipal solid waste, industrial solid waste, sludge frompaper manufacture, sewage sludge, residue from composting, food waste,spent distilling grain, spent Brewer's yeast, anaerobic digestive, yardwaste, wood and forestry waste. Additional examples of biomass include,but are not limited to, corn grain, corn cobs, crop residues such ascorn husks, corn stover, grasses including Miscanthus X giganteus,Miscanthus sinensis and Miscanthus sacchariflorus, wheat, wheat straw,hay, rice straw, switchgrass, waste paper, sugar cane bagasse, sorghum,soy, components obtained from milling of grains, trees (e.g. pine),branches, roots, leaves, wood chips, wood pulp, sawdust, shrubs andbushes, vegetables, fruits, flowers, animal manure, multi-componentfeed, and crustacean biomass (i.e., chitinous biomass). It may bepreferable to treat the biomass before use in the method of theinvention. For example the biomass could be mechanically treated e.g. bymilling or shredding.

Preferably, the treated cellulosic biomass is a treated lignocellulosicbiomass. “Treated cellulosic” or “treated lignocellulosic biomass” asused herein refers to wood or other cellulose or lignocellulosecontaining biomass which has been processed so that it contains metal ormetal ions (metal pollutants). For example it has been treated with apreservative or other metal-based formulation e.g. copper-basedfungicide. The preservative is preferably a metal based preservativesuch as one containing an alkaline copper quaternary (ACQ), copper azole(CA, Tanalith E), micronized copper quaternary (MCQ), or Chromatedcopper arsenate (CCA, Tanalith C). It also includes wood or othercellulosic or lignocellulosic biomass which has been painted for examplewith a lead-based paint, or paint containing titanium dioxide. Otherforms of treated cellulosic or lignocellulosic biomass include sewagesludge, which may contain cadmium (II) and/or mercury (I/11), wastepaper and municipal solid waste which may contain titanium as titaniumdioxide. Preferably the treated cellulosic biomass is a lignocellulosicbiomass, such as wood treated with a preservative.

A “metal pollutant” as used herein is a metal present within thecellulosic or lignocellulosic biomass which is not present in thecellulosic or lignocellulosic biomass in its natural state. The metalpollutant is preferably present as an oxidised metal compound or metalions. In particular it refers to a metal which inhibits the downstreamhydrolysis and/or fermentation of the cellulose rich material derivedfrom the cellulosic or lignocellulosic biomass. The metal is preferablyselected from zinc (II), lead (II), copper (II), arsenic (V), iron(II/III), titanium and chromium (VI). Preferably the metal is selectedfrom copper (II), arsenic (V) or chromium (VI), more preferably copper(II). The metal is preferably derived from a preservative.

The IL is preferably heated with the biomass at 100-180° C., preferably120-170° C. The reaction is carried out for 5 min-22 hours, preferably20 min-13 hours, more preferably 30 min-8 hours i.e. 10, 15, 20, 30, 45min, 1 hr, 2 hr, 3 hr, 4 hr, 5 hr, 6 hr, 7 hr, 9 hr, 10 hr, 11 hr, 12hr, 15 hr, 17 hrs, 20 hrs and ranges there between. Preferably themixture is stirred, for example at 50-200 rpm.

As used herein “ionic liquid” refers to an ionized species (i.e. cationsand anions). Typically they have a melting point below about 100° C. Itis important to choose an ionic liquid which is both thermally andchemically stable, so that is does not decompose during the treatmentprocess or electrodeposition. The ionic liquid comprises one or moreanion with one or more cation.

The anion is preferably selected from C₁₋₂₀alkyl sulfate [Alkyl SO₄]⁻,chloride [Cl]⁻, bromide [Br]⁻, hydrogen sulfate [HSO₄]⁻, hydrogensulfite [HSO₃]⁻, Trifluoromethanesulfonate [OTf]⁻ and acetate [OAc]⁻ ormixtures thereof. More preferably the anion is chloride [Cl]⁻, orhydrogen sulfate [HSO₄]⁻.

Preferably but not essentially, the lignin in the wood orlignocellulosic biomass is soluble in the ionic liquid at the treatmenttemperature, but the cellulose is not, so that a solid residue or pulpcomprising the cellulose is produced. Other components such ashemicellulose may preferably also dissolve in the ionic liquid. Themetal pollutants are retained in the ionic liquid.

The cation is preferably a protic cation ion, i.e. they are capable ofdonating a H⁺ (proton).

The cation ion can be an ammonium derivative. These cations have thegeneral formula

wherein

X is N; and

A¹ to A⁴ are each independently selected from H, an aliphatic, C₃₋₆carbocycle, C₆₋₁₀ aryl, alkylaryl, and heteroaryl.

Preferably at least one of A¹ to A⁴ is H. Preferably A¹ to A⁴ are eachindependently selected from H, and an aliphatic. In one embodiment oneof A¹ to A⁴ is H, and the remaining three are each independently analiphatic. Alternatively two of A¹ to A⁴ are each H and the remainingtwo are each independently an aliphatic. Alternatively one of A¹ to A⁴is an aliphatic, and the remaining three are all H. Preferably thecation is not ammonium (NH₄ ⁺.) i.e. at least one of A¹ to A⁴ is not H.

The term “aliphatic” as used herein refers to a straight or branchedchain hydrocarbon which is completely saturated or contains one or moreunits of unsaturation. Thus, aliphatic may be alkyl, alkenyl or alkynyl,preferably having 1 to 12 carbon atoms, preferably up to 6 carbon atomsor more preferably up to 4 carbon atoms. The aliphatic can have 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, or 12 carbon atoms.

The term “alkyl” as used herein, is typically a linear or branched alkylgroup or moiety containing from 1 to 20 carbon atoms, such as 11, 12,13, 14, 15, 16, 17, 18, or 19 carbon atoms. Preferably the alkyl groupor moiety contains 1-10 carbon atoms i.e. 2, 3, 4, 5, 6, 7, 8, 9, or 10carbon atoms such as a C₁₋₄ alkyl or a C₁₋₆ alkyl group or moiety, forexample methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl and t-butyl,n-pentyl, methylbutyl, dimethylpropyl, n-hexyl, 2-methylpentyl,3-methylpentyl, 2,3-dimethylbutyl, and 2,2-dimethylbutyl.

As used here in the term “alkenyl” refers to a linear or branchedalkenyl group or moiety containing from 2 to 20 carbon atoms, such as11, 12, 13, 14, 15, 16, 17, 18, or 19 carbon atoms. Preferably the alkylgroup or moiety contains 2-10 carbon atoms i.e. 3, 4, 5, 6, 7, 8, 9, or10 carbon atoms such as a C₂₋₄ alkenyl or a C₂₋₆ alkenyl group ormoiety, for example ethenyl, 2-propenyl, 1-propenyl.

The term “carbocycle” as used herein refers to a saturated or partiallyunsaturated cyclic group having 3 to 6 ring carbon atoms, i.e. 3, 4, 5,or 6 carbon atoms. A carbocycle is preferably a “cycloalkyl”, which asused herein refers to a fully saturated hydrocarbon cyclic group.Preferably, a cycloalkyl group is a C₃-C₆ cycloalkyl group.

The term “C₆₋₁₀ aryl group” used herein means an aryl group constitutedby 6, 7, 8, 9 or 10 carbon atoms and includes condensed ring groups suchas monocyclic ring group, or bicyclic ring group and the like.Specifically, examples of “C₆₋₁₀ aryl group” include phenyl group,indenyl group, naphthyl group or azulenyl group and the like. It shouldbe noted that condensed rings such as indan and tetrahydro naphthaleneare also included in the aryl group.

The terms “alkylaryl” as used herein refers to an alkyl group as definedherein substituted with an aryl as defined above. The alkyl component ofan “alkylaryl” group may be substituted with any one or more of thesubstituents listed above for an aliphatic group and the aryl orheteroaryl component of an “alkylaryl” or “alkylheteroaryl” group may besubstituted with any one or more of the substituents listed above foraryl, and carbocycle groups. Preferably, alkylaryl is benzyl.

The term “heteroaryl” as used herein refers to a monocyclic or bicyclicaromatic ring system having from 5 to 10 ring atoms, i.e. 5, 6, 7, 8, 9,or 10 ring atoms, at least one ring atom being a heteroatom selectedfrom O, N or S.

An aryl, heteroaryl, or carbocycle group as referred to herein may beunsubstituted or may be substituted by one or more substituentsindependently selected from the group consisting of halo, lower alkyl,—NH₂, —NO₂, —OH —COOH, or —CN.

The term “halogen atom” or “halo” used herein means a fluorine atom, achlorine atom, a bromine atom, an iodine atom and the like, preferably afluorine atom or a chlorine atom, and more preferably a fluorine atom.

Preferably the cation is an alkylammonium or a mixture thereof,preferably protic alkylammoniums, although aprotic alkylammoniums mayalso be used. Optionally one or more of the alkyl groups may besubstituted with —OH to form an alkanolammonium, which can also bereferred to as an alcoholammonium. As used herein an “alkylammonium”includes tetraalkylammoniums, trialkylammoniums, dialkylammoniums,monoalkylammoniums, and alcoholammoniums including trialcoholammoniums,dialcoholammoniums and monoalcoholammonium. Trialkylammoniums includetrimethylammonium, triethylammonium, and triethanolammonium. Examples ofdialkylammoniums include diethylammonium, diisopropylammonium, anddiethanolammonium. Monoalkylammoniums include methylammonium,ethylammonium, and monoethanolammonium.

Preferably the tetraalkylammonium is aprotic, i.e. not capable of actingas a proton donor.

Preferred alkylammonium cations are triethylammonium, diethylammoniumdimethylethylammonium, diethylmethylammonium, dimethylbutylammonium anddiethanolammonium.

The ionic liquid may contain one of the listed ammonium cations, or amixture thereof.

The cation can also contain a nitrogen-containing heterocyclic moietywhich, as used herein, refers to mono- or bicyclic ring systems whichinclude one nitrogen atom and optionally one or more further heteroatomsselected from N, S and O. The ring systems contain 5-9 members,preferably 5 or 6 members for monocyclic groups, and 9 or 10 members forbicyclic groups. The rings can be aromatic, partially saturated orsaturated and thus, includes both a “heteroalicyclic” group, which meansa non-aromatic heterocycle and a “heteroaryl” group, which means anaromatic heterocycle. The cation is preferably selected from

wherein R¹ and R² are independently selected from H, a C₁₋₆ alkyl or aC₁₋₆ alkoxyalkyl group, and R³, R⁴, R⁵, R⁶, R², R⁸ and R⁹, when presentare independently H, a C₁₋₆ alkyl, C₁₋₆ alkoxyalkyl group, or C₂₋₆alkyoxy group. Preferably R¹ and R² are C₁₋₄ alkyl, with one beingmethyl and R³—R⁹, (R³, R⁴, R⁵, R⁶, R², R⁸ and R⁹), when present, are H.Preferably the cation ring is imidazolium or pyridinium.

“C₂₋₆ Alkoxy” refers to the above C₁₋₆ alkyl group bonded to an oxygenthat is also bonded to the cation ring. A “C₂₋₆ alkoxyalkyl group”refers to an alkyl containing an ether group, with the general formulaX—O—Y wherein X and Y are each independently a C₁₋₅ alkyl and the totalnumber of carbon atoms is between 2 and 6 e.g. 2, 3, 4, 5, or 6.

Preferred cations are imidazolium based cations or a mixture thereof inparticular protic imidazolium based cations. Preferably the imidazoliumbased cations is selected from 1-ethyl-3-methylimidazolium ([EMIM]⁺),1-butylimidazolium ([HBIM] 1 and 1-methylimidazolium ([HMIM]⁺, alsoreferred to as [HC₁im]⁺ herein) or a mixture thereof.

Preferred cations include protic alkylammonium, proticmethylimidazolium, protic pyridinium, aprotic tetraalkylammonium andaprotic dialkylimidazolium ions.

The ionic liquid may contain one of the listed cations, or a mixturethereof.

Preferred ionic liquids for use in the invention are triethylammoniumhydrogen sulfate [TEA][HSO₄], N,N-dimethyl-N-butylammonium hydrogensulfate [DMBA][HSO₄], 1-methylimidazolium hydrogen sulfate [HMIM][HSO₄],I butylimidazolium hydrogen sulfate [HBIM][HSO₄], diethylammoniumhydrogen sulfate [DEA][HSO₄], diethanolammonium Chloride [DEtOHA][Cl],1-methylimidazolium hydrogen chloride [HMIM][Cl],1-ethyl-3-methylimidazolium chloride [EMIM][Cl],1-ethyl-3-methylimidazolium acetate [EMIM][OAc],1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMIM][OTf].Particularly preferred ionic liquids are 1-methylimidazolium hydrogensulfate [HMIM][HSO₄] and 1-methylimidazolium chloride [HMIM][Cl].

Ionic liquids can be prepared by methods known to the person skilled inthe art or obtained commercially. For example, the ILs can be made froma simple alkylamine, such as triethylamine, and sulfuric acid in aone-step synthesis, for example as described in George et al., (2015)“Design of low-cost ionic liquids for lignocellulosic biomass treatment”Green Chemistry 17:1728-173.

Usually in an ionic liquid the cation and anion are present in equimolaramounts. However, the ionic liquid may preferably comprise excess base,preferably protonated base. ‘Base’ as used herein refers to the basefrom which the cation is derived e.g. amine/imidazole. Preferably theionic liquid comprises 10% molar excess base, preferably 4-8%, 5-7.5%excess base. The ionic liquid may comprise 2%, 3%, 4%, 5%, 6%, 7%, 8% 9%or 10% molar excess base.

It has been surprisingly found that the yield in the saccharificationstep can be improved if the ionic liquid composition comprises water.Therefore in one preferred embodiment the composition comprises the ILand 10-40% v/v water. Preferably the composition comprises 20-30% v/vwater. Water is added at around 20% to prevent reactions between IL andtreated cellulosic or lignocellulosic biomass, reduce viscosity andpromote depolymerisation of lignin.

It has also been discovered that the presence of an excess of acidaccelerates the pre-treatment resulting in improved lignin removal andthus enhanced saccharification yields, as lignin interferes with theenzyme binding. Thus, the glucose yield is improved. Therefore in onepreferred embodiment the composition further comprises 0.01-20% molarexcess acid, preferably 1-5% molar excess acid, as a percentage of theIL. The addition of a small amount of acid significantly accelerates thepre-treatment process, when other variables such as water content andtemperature are kept constant. The acid can be selected from any knownstrong acid such as hydrochloric acid, sulfuric acid, nitric acid,phosphoric acid hydroiodic acid, perchloric acid and hydrobromic acid.Preferably the acid is sulfuric or, hydrochloric or phosphoric acid.

In a preferred embodiment the treated cellulosic or lignocellulosicbiomass is contacted with the ionic liquid composition prior tomechanical treatment. It has been found that contacting the treatedcellulosic or lignocellulosic biomass with the ionic liquid can reducethe energy required to grind the treated cellulosic or lignocellulosicbiomass. The IL composition appears to work as a lubricant during thegrinding phase. The treated cellulosic or lignocellulosic biomass can beimpregnated briefly with an IL composition at slightly elevatedtemperature (70-100° C., preferably 90° C.) to harness their lubricationproperties before a mechanical size reduction step is applied. The ILcomposition can be contacted with the treated cellulosic orlignocellulosic biomass for any length of time from several minutes to18 hours or longer, preferably 5 minutes to 1 hour. This can be followedby further treatment with an ionic liquid composition as describedherein to extract the metal pollutants and also solubilise the lignincontent of the treated lignocellulosic biomass.

This invention adds a novel aspect to the fractionation of cellulosic orlignocellulosic biomass with ionic liquids by integrating the celluloseor lignocellulose fractionation with pollutant metal extraction. Asdescribed in the examples, pre-treatments with an ionic liquid ofsoftwood impregnated with a copper-based preservative achieved up to 98%removal of the Cu^(II) in a single pass.

The metal can be recovered from the IL, thereby providing an additionalincome stream, and by removing the metal pollutant increases the valueof biomass utilised, as the cellulosic or lignocellulosic biomass willbe converted from a negative-value waste into a positive-value fuelresource (FIG. 1). Cellulosic biofuel production and hazardous wastewood processing in one step has not been described previously.

Ionic liquids are highly conductive solvents due to their ionic natureand regarded as superior media for the electrodeposition of metals andsemiconductors. Key advantages that enable the ILs to overcome thelimits imposed by common aqueous or organic media are their wideelectrochemical windows, spanning up to 6 V in some cases; low vapourpressures, which allow electrodeposition at temperatures well above 100°C., and numerous, only partly understood, cation/anion effects that makeit possible to influence the morphology and crystal size of deposits.Electrodeposition is currently not practised for the recovery of metalsfrom dilute heavy metal-containing IL waste streams.

The process may preferably further comprise electrodeposition of themetal pollutant from the ionic liquid. The electrodeposition can becarried out by applying an appropriate current per unit electrode areafrom a transformer-rectifier, as used industrially for recovery of manymetals from aqueous electrolyte solutions. Other suitable methodsinclude chronoamperometry and chronopotentiometry. Electrodepositionallows the metal pollutant to be recovered as a solid metal or alloy.Recovery of metals by electrodeposition provides an added revenue streamwhich could provide $10 worth (assuming a price of $5,000 (tonne Cu)⁻¹)of Cu⁰ per tonne of treated wood (containing 2000 ppm of Cu^(II)). Theelectrical energy costs required for the process are estimated as anorder of magnitude lower than the value of the recovered copper. Theprocess also eliminates the need to landfill metal containing ashes. Inaddition recycling of metals may contribute to a reduced reliance onforeign imports of metals (strengthen local resource resilience) andalso reduce the environmental impact of mining.

After the electrodeposition process, the ionic liquid can be recycled orre-used to process further treated cellulosic or lignocellulosic biomassin step (a) and/or step (ci).

The ionic liquids of the present invention dissolve the lignin withinthe biomass but do not dissolve the cellulose. The majority of celluloseremains solid, preferably at least 90%, more preferably 95%. It can beeasily removed from the liquid phase mechanically, for example byfiltration. The separated solid residue or pulp can then be washed andused in the saccharification process. This removes the need for aseparate precipitation step to obtain the cellulose once the biomass hasbeen treated. Thus the method of the invention may preferably furthercomprise the step of separating the ionic liquid from the cellulosecontaining solid residue produced in step (a) from the ionic liquid.

The cellulose containing solid residue may be washed with ionic liquidor an organic solvent miscible with the ionic liquid. The separationefficiency and the ionic liquid recovery can be enhanced by washing thecellulose containing solid residue with ionic liquid or an organicsolvent that is miscible with the ionic liquid. Examples of suitableorganic solvents include aliphatic alcohols such as methanol andethanol. After washing, the organic solvent can be separated from thecellulose containing solid residue, and added to the ionic liquid fromstep (a). The organic solvent is removed before or potentially after thelignin is precipitated. The organic solvent can be removed from theionic liquid using conventional methods known to the skilled person. Forexample the volatile organic solvents can be removed by distillation.

It is possible to precipitate the lignin dissolved in the ILcompositions. Therefore the method may further comprise

-   -   (d) adding an anti-solvent to the ionic liquid which has been        separated from the cellulose containing solid residue produced        in step (a), to precipitate out the dissolved lignin and        optionally separating the precipitated solid from the        anti-solvent/ionic liquid.

As used herein an “anti-solvent” or precipitate is a liquid which causesthe lignin to precipitate out from the ionic liquid containing thesolubilised lignin produced in step (a). The anti-solvent is preferablywater or ethanol. The ionic liquid can be recovered by removing theanti-solvent, for example by evaporation. The resulting ionic liquid canthen be recycled to be used again in the method. Thus the method mayfurther comprise removing the anti-solvent from the ionic liquidobtained in (d).

The ionic liquid may need to be dried to remove excess water. The watermay be removed by conventional methods such as evaporation. The watermay be removed after step (a) and/or after the lignin has beenprecipitated. As the presence of some water improves the yield lessenergy is required to dry the IL.

The cellulose containing solid residue obtained from the method of theinvention can undergo saccharification, for example by enzymatichydrolysis, to obtain glucose. The glucose can then be used in afermentation process to obtain biofuel. Therefore the process canfurther comprise saccharification of the cellulose containing solidresidue to obtain glucose. The cellulose containing solid residue usedin the saccharification step may be the cellulose containing solidresidue obtained in the initial step, step (a), or the washed solidresidue obtained in step (c). The invention also provides a cellulosecontaining solid residue obtained by a suitable method of the invention;for example as obtained by the process comprising any one or more ofsteps (a-c). In a further aspect the invention provides a process ofpreparing glucose from treated cellulosic or lignocellulosic biomasscomprising subjecting a cellulose containing solid residue obtained bysuitable methods of the invention to enzymatic hydrolysis. In a furtheraspect the invention provides glucose obtained by this hydrolysis.

Suitable enzymes for use in the process include commercially availablepreparations of cellulases such as T. reseei cellulase and Novozyme 188cellobiase that also contains hemicellulolytic activity. Other usefulenzymes include esterases, either acetyl esterases or feruloylesterases, which cleave substituents that are esterified tohemicellulose. The process is preferably carried out in an aqueousmedium at a suitable pH for the enzymes. The conditions can be optimisedin relation to pH, temperature and the medium used depending on theenzyme mixture required. Such methods are well known to the skilledperson. The process is preferably carried out in accordance with“Enzymatic saccharification of lignocellulosic biomass”(NREL/TP-510-42629), issue date Mar. 21, 2008.

In summary the process of the invention may comprise the followingsteps:

-   -   (a) contacting the treated cellulosic or lignocellulosic biomass        with an ionic liquid, said ionic liquid comprising an anion and        a cation;    -   (b) optionally separating the cellulose containing solid residue        obtained in step (a) from the ionic liquid;    -   (c) optionally washing the cellulose containing solid residue at        least once with ionic liquid or an organic solvent miscible with        the ionic liquid; and separating the cellulose containing solid        residue from the ionic liquid or organic solvent and optionally        adding the ionic liquid or organic solvent to the ionic liquid        obtained in (b);    -   (d) optionally adding an anti-solvent to the ionic liquid        obtained in (b) to precipitate the lignin;    -   (e) optionally removing water from the ionic liquid, after        step (b) and/or after step (d);    -   (f) electrodeposition of the metal pollutant from the ionic        liquid obtained in steps (b), and/or (c) and/or (e);    -   (g) optionally recycling the ionic liquid after step (f) to be        used in step (a) and/or step (c); and    -   (h) optionally saccharification of the cellulose containing        solid residue obtained in any of steps (a), (b) and/or (c) to        obtain glucose.

The invention further provides for the use of an ionic liquid as definedherein to extract metal from a treated cellulosic or lignocellulosicbiomass source, preferably a wood source which has been treated with apreservative, in particular a metal based preservative. The inventionfurther provides the use of an ionic liquid as defined herein, ins amethod of extraction metal from a treated cellulosic or lignocellulosicbiomass source as described herein.

The invention will now be described in the examples below which refer tothe following figures:

FIG. 1 is a flow chart of the biomass pre-treatment and copperextraction process. CRM stands for Cellulose Rich Material.

FIG. 2 displays the composition of the copper (II) treated wood asanalysed by compositional analysis.

FIG. 3 shows copper (II) concentrations in IL measured by inductivelycoupled plasma optical emission spectrophotometry ICP OES

FIG. 4 shows currents measured at −1V in [HC₁im][HSO₄].

FIG. 5 shows cyclic voltammograms of recycled and fresh [HC₁im][HSO₄]doped with CuO to saturation;

The temperature and time period are not essential for the extraction ofthe copper (II), but they will have a major impact on the sugar yieldsachieved from enzymatic saccharification of the pulps.

EXAMPLE 1. DECONSTRUCTION OF BIOMASS AND EXTRACTION OF METALS IN VARIOUSIONIC LIQUIDS

A flow chart of the deconstruction and extraction process is summarizedin FIG. 1. An ionic liquid/water mixture was prepared by adding therequired amount of water to the dried ionic liquid. The water contentwas confirmed by Karl-Fischer titration in triplicate. Pre-treatmentswere run in triplicate. 10±0.05 g of ionic liquid/water master-mix wasweighed into a glass pressure tube and the exact weight recorded. Copperazole treated softwood (1.0 g oven-dried basis) with particle sizes of180-850 μm was added and the tube tightly closed and the contents mixedwith a Vortex shaker until all of the biomass had been in contact withthe ionic liquid. The vial was placed in a preheated convection oven at170° C. for 30 min. After the incubation, the mixture was transferredinto a 50 mL centrifuge tube. This was facilitated by diluting with 40mL of ethanol. The contents were mixed using a vortex shaker and left atroom temperature for one hour. The tube was then centrifuged and thesolids and liquids decanted carefully into a round bottom flask. Thesolid was further washed by repeating the washing step 2-3 more times.The remaining solid (pulp) was then transferred into a cellulose thimbleand further washed by Soxhlet extraction with refluxing ethanol (150 mL)for 22 hours. The pulp was left to dry in the thimble on the benchovernight. The ethanol used for the Soxhlet extraction was combined withthe previous washes and evaporated under reduced pressure at 40° C.,leaving the dried ionic liquid/lignin mixture. To the dried ionicliquid/lignin mixture, 30 mL of water was added in order to precipitatethe lignin. The suspension was transferred into a 50 mL falcon tube,shaken for one minute and then left at room temperature for at least 1hour. The tube was centrifuged and the supernatant decanted andcollected in a round bottom flask. This washing step was repeated threemore times and the washings combined.

The air-dried pulp yield was determined by weighing the recoveredbiomass from the cellulose thimbles. The oven-dried yield was determinedas described below. The lid of the centrifuge tube containing the ligninwas pierced and the tube put into a vacuum oven overnight for drying thelignin at 40° C. under vacuum. The dried lignin was weighed the next dayto determine the lignin yield.

Saccharification

Enzymatic saccharification was performed in triplicate according to LAP“Enzymatic saccharification of lignocellulosic biomass”(NREL/TP-510-42629), issue date Mar. 21, 2008. The enzymes wereNovozymes experimental enzyme mixture NS-22201. Glucose yields werecalculated based on the glucose content of the untreated biomass. 50 μLof enzyme solution was used per 100 mg of sample.

Compositional Analysis

The glucan, hemicellulose and lignin content of copper treated timberwas determined following the LAP procedures “Preparation of samples forcompositional analysis” (NREL/TP-510-42620), issue date Aug. 6, 2008 andDetermination of Structural Carbohydrates and Lignin in Biomass”(NREL/TP-510-42618 version Aug. 3, 2012). The extractives in untreatedcopper treated timber were removed and quantified according to the LAP“Determination of extractives in biomass” (NREL/TP-510-42619), issuedJul. 17, 2005. The oven-dry weight (ODW) of lignocellulosic biomass wasdetermined according to the procedure described in the LAP“Determination of Total Solids in Biomass and Total Dissolved Solids inLiquid Process Samples” (NREL/TP-510-42621) issued Mar. 31, 2008.

Metal Content

Inductively coupled plasma optical emission spectrophotometry (ICP-OES)was used to analyse the ionic liquid liquor on its metal content and runin triplicate on a Perkin Elmer Optima 2000 DB instrument. A mixed metalstandard for ICP analysis was obtained from Sigma Aldrich (TraceCERTgrade) and diluted to the required concentrations with 5% nitric acid.

The water content of the ionic liquid liquors was determined byKarl-Fischer titration. The liquors were diluted to below 10 ppm ofcopper and a maximum of 1 wt % ionic liquid concentration with 5% nitricacid and then analysed by ICP-OES.

Approximately 100 mg of ground wood samples were weighed out and theexact weight recorded (±0.1 mg, Mettler Toledo NewClassic MS). Thesamples were digested in 1 mL 69% nitric acid in a closed PTFE vessel(MARSXpress vessels and microwave with power/time control by CEM withthe following sequence: 300 W at 83% power for 5 min, 600 W at 66% powerfor 5 min and 1200 W at 58% power for 6 min). The obtained solution wascooled in a freezer for an hour before diluting to 10 mL with 5% nitricacid and filtration through a 0.4 μm PTFE syringe filter.

The measured wood's copper content was used to calculate the percentageof copper extracted into the ionic liquid.

Results and Discussion

Ionic Liquid Screening Experiments for the Extraction of Copper(II) fromCA Treated Softwood

FIG. 2 displays the composition of the copper treated wood as analysedby compositional analysis.

TABLE 1 Composition of copper treated wood used in pre-treatments. Glustands for glucan, Xyl for xylan, Gal for galactan, Ara for arabinan,Man for mannan, AIL for acid insoluble lignin, ASL for acid solublelignin, Extr. for extractives. Glu Xyl Gal Ara Man AIL ASL Ash Extr.47.9 ± 0.8 6.5 ± 0.1 0.8 ± 0.0 0.4 ± 0.0 13.6 ± 0.3 25.4 ± 1.1 3.3 ± 0.1BDL 2.1 ± 0.0

The following ionic liquids were screened for their suitability tofractionate/pre-treat biomass and to extract copper from the biomass,where [TEA] stands for triethylammonium, [DMBA] forN,N-dimethyl-N-butylammonium, [DEA] for diethylammonium, [DEtOHA] fordiethanolammonium, [HMIM] for 1-methylimidazolium and [EMIM] for1-ethyl-3-methylimidazolium:

TABLE 2 Ionic liquids screened. Ionic liquid Type of ionic liquid[TEA][HSO₄] Protic, symmetric, tertiary amine based, weakly coordinatinganion [DMBA][HSO₄] Protic, asymmetric, tertiary amine based, weaklycoordinating anion [HMIM][HSO₄] Protic, imidazole based, weaklycoordinating anion [DEA][HSO₄] Protic, symmetric, secondary amine based,weakly coordinating anion [DEtOHA][Cl] Protic, symmetric, secondaryamine based, alcohol side chain, strongly coordinating anion [HMIM][Cl]Protic, imidazole based, strongly coordinating anion [EMIM][Cl] Aprotic,imidazole based, strongly coordinating anion [EMIM][OAc] Aprotic,imidazole based, strongly coordinating anion [EMIM][OTf] Aprotic,imidazole based, mildly coordinating anion

Table 3 displays the copper (II) extraction, saccharification yield aswell as pulp and lignin yields after pre-treatment of the copper azoletreated softwood with the tested ILs as a percentage of the totalinitial biomass.

TABLE 3 Results from screening experiments. Sacchar- Copper ificationPulp Lignin Ionic liquid extraction/% yield/% yield/% yield/%[TEA][HSO₄] 87 ± 1 55.2 ± 2.6 56.7 ± 0.3 8.7 ± 0.2 [DMBA][HSO₄] 93 ± 072.3 ± 4.1 42.6 ± 0.3 19.4 ± 1.4  [HMIM][HSO₄] 82 ± 1 15.7 ± 2.6 58.9 ±0.5 7.0 ± 1.7 [HMIM][Cl] 98 ± 2 75.7 ± 2.5 43.1 ± 0.8 14.3 ± 0.7 [DEA][HSO₄] 85 ± 2  0.1 ± 0.1 34.7 ± 1.0 7.3 ± 0.4 [DEtOHA][Cl] 81 ± 411.0 ± 0.3 94.5 ± 0.3 BDL [EMIM][OAc] 86 ± 2 43.0 ± 1.9 92.1 ± 1.2 BDL[EMIM][Cl] 92 ± 1 28.8 ± 2.9 75.9 ± 1.8 1.7 ± 0.2 [EMIM][OTf] 68 ± 1 9.7 ± 0.3 92.7 ± 0.4 BDL Untreated —  9.9 ± 0.2 100 —

The data shown here suggests that [HSO₄]⁻, [Cl]⁻ and [OAc]⁻ ILs arecapable of the extraction of 81-98% of the present copper (II) fromtreated softwood. The only IL studied here that extracted significantlylower amount of copper was [EMIM][OTf] which extracted 68% of the copper(II). A wider range of results was obtained for the saccharification ofthe recovered cellulose rich pulp; the highest glucose yields wereobtained for enzymatic saccharification of [DMBA][HSO₄] and [HMIM][Cl]pre-treated biomass (above 70% of theoretical). Lower yields but stillsignificant improvements compared to untreated biomass were obtainedwith [TEA][HSO₄], [EMIM][OAc] and [EMIM][Cl].

CCA Treated Wood

Pre-treatments of chromated copper arsenate (CCA) treated softwood with[HBIM][HSO₄], where [HBIM] stands for 1-butylimidazolium, were conductedat 170° C. for 30 min. Saccharification yields obtained were 52.5% andthe metal extraction is displayed in table 4. All three metals wereextracted nearly quantitatively (≥98%).

TABLE 4 Metal Contents as measured by ICP-OES and relative metalextraction in pulp after [HC₄im][HSO₄] pre-treatment of the CCA treatedwood for 1 hour at 150° C. Standard error of measurements in brackets.CCA Treated Wood Arsenic(V) Chromium(VI) Copper(II) Metal Content/ppm4268 (605)   4664 (745)   2784 (365)   Metal Extracted 99% (0.06%) 99%(0.14%) 98% (0.46%)

Mixed Infeed and Processed Wood

Mixed unprocessed and processed wood waste obtained (unprocessed wood ischipped waste wood of various origin, processed wood is the same type ofwood that had part of the metals, mainly iron, removed mechanically)were pre-treated at 170° C. for 30 min with two different ILs,[HC₁im][Cl] and [HC₁im][HSO₄]. The original metal content as well as theamounts extracted for unprocessed and processed wood are displayed inTables 5 and 6 respectively. Higher saccharification yields wereobtained with [HC₁im][Cl] and measured to be 53 and 60% for unprocessedand processed wood respectively.

TABLE 5 Metal Contents as measured by ICP-OES and relative metalextraction in pulp after pre- treatment of the unprocessed mixed wood.Standard error of measurements in brackets. Unprocessed Mixed WoodZinc(II) Lead(II) Iron(II/III) Chromium(VI) Copper(II) Metal Content/ppm138 (0.3)  173 (8.4)  567 (12.4)  9.1 (1.2)  37 (6.9)  Metal Extractedwith 82% (1.50%) 12% (1.85%) 55% (3.67%) 69% (1.71%) 54% (2.07%)[HC₁im][HSO₄] Metal Extracted with 86% (3.02%) 85% (1.29%) 65% (4.67%)80% (3.46%) 90% (0.59%) [HC₁im][Cl]

TABLE 6 Metal Contents as measured by ICP-OES and relative metalextraction in pulp after pre- treatment of the processed mixed wood.Standard error of measurements in brackets. Processed Mixed WoodZinc(II) Lead(II) Iron(II/III) Chromium(VI) Copper(II) Metal Content/ppm114 (0.3)  367 (18.7)  331 (31.7)  55 (2.1)  82 (5.0)  Metal Extractedwith 70% (6.20%) 39% (4.47%) 52% (14.86%) 77% (2.66%) 48% (2.74%)[HC₁im][HSO₄] Metal Extracted with 89% (0.41%) 96% (1.92%) 56% (9.28%) 93% (0.54%) 97% (0.29%) [HC₁im][Cl]

The presented results suggest very high extraction efficiencies in therange of 80-99%, for zinc (II), lead (II), chromium (VI) and copper (II)are possible with [HC₁im][Cl] in the absence of a chelating agent.

EXAMPLE 2 COPPER SOLUBILITY AND ELECTRODEPOSITION OF COPPER FROM VARIOUSIONIC LIQUIDS COPPER SOLUBILITY

Solubility measurements were conducted in order to establish solubilitylimits in one of the investigated protic ionic liquids1-methylimidazolium hydrogen sulfate ([HC₁im][HSO₄], shown below, top).For comparison, solubility was also tested in the more inexpensivetriethylammonium hydrogen sulfate [TEA][HSO₄] (shown below, bottom).

The solubilities were tested by dissolving copper oxide in the ionicliquid until no further dissolution was observed overnight. Theremaining solids were filtered off and the obtained solutions subjectedto ICP-OES. In order to investigate if excess base improvedsolubilities, 5 wt % excess amine/imidazole was used in a further test.The results are displayed in FIG. 3. The maximum copper(II) solubilitiesat 20 wt % water are also summarised in table 7.

TABLE 7 Copper(II) solubilities in ionic liquid systems at 20 wt %water. Ionic Liquid Copper(II) solubility/ppm [HC₁im][HSO₄] 4752 ± 715[TEA][HSO₄] 2043 ± 433 [HC₁im][HSO₄] 5% excess base 10845 ± 2050[TEA][HSO₄] 5% excess base 13712 ± 4068

FIG. 3 shows that the water content plays a deciding role in the copperdissolution capability of the ionic liquid. Solubility peaks at around60 wt % and 80 wt % water in the case of [HC₁im][HSO₄] and [TEA][HSO₄]respectively. Peak solubility is around 72,000 ppm or 7.2 wt % in thecase of [HC₁im][HSO₄] and 33,000 ppm or 3.3 wt % in the case of[TEA][HSO₄]. At higher base contents the dissolution capacity of[HC₁im][HSO₄] is improved to around 93,000 ppm or 9.3 wt % at 60 wt %water. Pre-treatments however cannot be conducted at water contentsabove around 30% which means that solubilities at around 20 wt % waterare more important for the here conducted study. From table 7 we can seethat at 20 wt % water the solubility in [HC₁im][HSO₄] was improved from4752 ppm to 10845 ppm by the addition of 5% excess base while in thecase of [TEA][HSO₄] dissolution capability was improved from 2043 ppm to13712 ppm. [HC₁im][HSO₄] and [TEA][HSO₄] with 5 wt % excess basetherefore reach a similar dissolution capacity within the measurementerror.

While these tests were conducted by dissolving Cu(II) oxide, copperbound in the biomass is expected to be extracted in a similar manner.

Electrochemical properties of [HC₁im][HSO₄]

For a successful deposition of copper from the ionic liquid,electrochemical stability of the IL needs to be guaranteed in order tomake the process viable. FIG. 4 shows maximum currents obtained at −1 Vvs. Ag in [HC₁im][HSO₄] with different water contents. The almost dry IL(2 wt % water) shows very small currents at very reducing potentials,suggesting that the ionic liquid is electrochemically stable under theseconditions. The higher water content ILs exhibit higher currentdensities due to the occurrence of water reduction leading to hydrogenevolution. The current density reaches a maximum at 25 wt % water andthen decreases again. The hydrogen evolution reaction can be linked toacidity of the medium. The data presented here suggest that acidity ofthe ionic liquid maximises at around 25 wt % water.

Copper Deposition

The deposition of copper out of an ionic liquid liquor was shown for[HC₁im][HSO₄] as well as for the less expensive triethylammoniumhydrogen sulfate ([TEA][HSO₄]) by means of cyclic voltammetry andchronoamperometry. In both cases, liquor from biomass pre-treatment wassaturated with copper (II) ions by dissolution of CuO and filtering offundissolved solid. The liquors tested contained 20 wt % water in orderto mimic the conditions of pre-treatment.

Preliminary results of solubility tests of CuO in the two protic ionicliquids show a higher solubility in the imidazolium salt than in thealkylammonium salt. Therefore the focus of further tests has been on theimidazolium salt. In order to establish the effect of biomassdegradation products present in the liquor on the deposition behaviourof copper, a cyclic voltammogram (FIG. 5) of copper (II) saturated freshionic liquid was compared to that obtained from the copper (II)saturated recycled ionic liquid. The oxidation current peak due toCu→Cu^(II)+2e⁻ at ca. 0.1 V in the positive-going voltammetric scan ofthe recycled liquor was shifted slightly towards higher potentialscompared to the fresh ionic liquid and exhibited a small side peakbefore the main peak. However, the potentials (ca. −0.15 V) of currentonsets for the oxidation (Cu→Cu^(II)+2e⁻) and reduction (Cu^(II)+2e⁻→Cu)were almost identical. Integration of current-time data furtherconfirmed that the copper deposition was not measurably affected bybiomass degradation products, as charge efficiencies in both cases werearound 94% under the tested conditions.

1. A process for the extraction of metal pollutants from treatedlignocellulosic biomass, the process comprising (a) contacting thetreated lignocellulosic biomass with an ionic liquid, said ionic liquidcomprising an anion and an organic cation, wherein the contactingproduces a cellulose-rich solid material and a liquid phase, wherein theliquid phase comprises a hemicellulose fraction, a lignin fraction, andmetal pollutants.
 2. The process of claim 1 wherein the anion isselected from C₁₋₂₀ alkyl sulfate ([alkyl SO₄]⁻), chloride (Cl⁻),bromide (Br⁻), hydrogen sulfate ([HSO₄]⁻), hydrogen sulfite ([HSO₃]⁻),trifluoromethanesulfonate ([OTf]⁻) and acetate ([OAc]⁻).
 3. The processof claim 2 wherein the anion is selected from chloride (Cl⁻), acetate([OAc]⁻), and hydrogen sulfate ([HSO₄]⁻).
 4. The process of claim 1wherein the cation is selected from (i) a cation of general formula:

wherein X is N; and A¹ to A⁴ are each independently selected from H, analiphatic, C₃₋₆ carbocycle, C₆₋₁₀ aryl, alkylaryl, and heteroaryl; or(ii) a cation containing a nitrogen-containing heterocyclic moiety. 5.The process of claim 4 wherein at least one of A¹ to A⁴ is H.
 6. Theprocess of claim 1 wherein the organic cation is a protic organiccation.
 7. The process of claim 1 wherein the cation is analkylammonium, an alcoholammonium, or a mixture thereof.
 8. The processof claim 7 wherein the cation is N,N-dimethyl-N-butylammonium ([DMBA]⁺).9. The process of claim 4 wherein the cation containing anitrogen-containing heterocyclic moiety is an imidazolium based cationor a mixture thereof.
 10. The process of claim 9 wherein the imidazoliumbased cation is selected from 1-ethyl-3-methylimidazolium ([EMIM]⁺),1-butylimidazolium ([HBIM]⁺) and 1-methylimidazolium ([HMIM]⁺).
 11. Theprocess of claim 1 wherein the ionic liquid is selected from[DMBA][HSO₄], [HBIM][HSO₄], [HMIM][HSO₄], or [TEA][HSO₄], or mixturesthereof.
 12. The process of claim 1 wherein the organic cation isderived from its conjugate base, and wherein the ionic liquid comprisesat least 5% molar excess of the conjugate base.
 13. The process of claim1 wherein the ionic liquid is contacted with the biomass in the form ofa composition comprising the ionic liquid and 10-40% v/v water.
 14. Theprocess of claim 1 further comprising (b) separating the cellulose-richsolid material from the liquid phase.
 15. The process of claim 14further comprising (c(i)) washing the cellulose-rich solid material atleast once with a washing fluid that is the ionic liquid or an organicsolvent miscible with the ionic liquid.
 16. The process of claim 15further comprising (c(ii)) separating the cellulose-rich solid materialfrom the washing fluid.
 17. The process of claim 14 further comprising(d) adding an anti-solvent to the ionic liquid obtained in (b) toprecipitate the lignin.
 18. The process of claim 14 further comprisingremoving water from the ionic liquid after step (b).
 19. The process ofclaim 17 further comprising removing water from the ionic liquid afterstep (d).
 20. The process of claim 1 further comprisingelectrodeposition of the metal pollutant from the ionic liquid.
 21. Theprocess of claim 20 wherein after the electrodeposition, the ionicliquid is re-used in step (a).
 22. The process of claim 15 furthercomprising electrodeposition of the metal pollutant from the ionicliquid, wherein after the electrodeposition, the ionic liquid is re-usedin step (c(i)).
 23. The process of claim 1 further comprisingsaccharification of the cellulose containing solid residue obtained instep (a) to obtain glucose.
 24. The process of claim 14 furthercomprising saccharification of the cellulose containing solid residueobtained in step (b) to obtain glucose.
 25. The process of claim 16further comprising saccharification of the cellulose containing solidresidue obtained in step (c(ii)) to obtain glucose.
 26. A method offractionating lignocellulosic biomass, the method comprising: (a)contacting the lignocellulosic biomass with an ionic liquid, said ionicliquid comprising an anion and a N,N-dimethyl-N-butylammonium ([DMBA]⁺)cation.
 27. The method of claim 26, wherein the ionic liquid isN,N-dimethyl-N-butylammonium hydrogen sulfate ([DMBA][HSO₄]).